The use of Coomassie Brilliant Blue G-250 for staining electrophoresis gels to a defined endpoint is possible because the dye can be formulated as a colloidal form that does not enter the gel for staining, but rather is adsorbed by the protein bands in the gel, saturating the bands given enough time to diffuse throughout the bands. The fact that the colloidal form does not enter the gel itself makes the background very low, and lowers the need for a destaining step, which can result in decreased intensity of the stained protein bands.
Typically, a two-part stain is used to stain electrophoesis gels. The two-part stain must be made fresh before each use to have the desired performance (e.g., low background). Two-part stains quickly form a precipitate that renders the solution unusable—typically in 24 hrs. Two-part stain formulations are also based on using methanol as the alcohol. Simply replacing methanol with ethanol will render the formulation to have unacceptable performance.